Pervious concrete is a no-fines, cavity-rich concrete. The cavity volume of pervious concrete is between 10 and 35 vol. %, preferably 20 to 25 vol. %. The no-fines pores arise through the use of fillers of narrowly limited particle size group, wherein usually only a single particle size group is used (uniform grain size, such as for example 5/8 mm chippings) and with almost complete reduction of the content of fine components. Pervious concrete has just sufficient cement binder that the individual grains of the aggregate are only cemented together at the contact sites by a thin hardened cement layer and after compaction the cavities between the individual grains are still not filled. Open-pore concrete (pervious concrete) is in particular used for noise reduction in infrastructure projects, for example in road construction, in order to construct low-noise pavements. In addition, because of its open-pore nature, pervious concrete is also used for drainage in seepage-prone traffic areas, for example parking lots, exhibition areas and cycle routes. The longevity of these pavement systems is limited owing to the formation of cracks and particle escape. In order to remedy these defects, pervious concrete is modified with polymer dispersions.
In pervious concrete layers, the use of polymers leads to an improvement in the freeze-thaw resistance, crack resistance and less particle escape, and thus increases the stability of the pervious concrete layer and its lifetime. What is decisive here is that the flexibility of the concrete matrix is sufficiently increased and thus crack formation and grain escape are minimized, but at the same time the mechanical strength is also maintained, in order sufficiently to ensure the durability of the concrete.
In DE-OS 1953158, a water-permeable porous concrete is described which is produced from granular mineral aggregates of a uniform grain fraction, a binder such as cement and a water-soluble macromolecular substance and if necessary an aqueous dispersion of a thermo-plastic resin such as polyvinyl acetate. However, this system does not meet the requirements for the durability of water-permeable and noise-absorbing road surfaces, since the water-soluble macromolecular substances can be washed out by rainwater and pure polyvinyl acetate becomes brittle at low temperatures of <10° C.
In DE 102004006165 A1, a multilayer open-pore floor covering is described, the top open-pore layer whereof is incorporated with one or two component polyurethane or epoxide adhesives as binders. The costly incorporation of the whole system in several layers, and the use of polyurethane or epoxide adhesives as binders, without cheaper mineral binders such as cement, make the floor covering expensive and not widely utilizable. Moreover, polyurethane and epoxide adhesives are not ecologically problem-free.
The subject of EP 0710633 B1 is a pervious concrete which contains a polymeric binder in the form of an anionic styrene/(meth)acrylate copolymer. The styrene-acrylate copolymers used should preferably have a high minimum film-forming temperature (MFT) in the range from 35° C. to 50° C. Such styrene copolymers are rigid polymers, which do not sufficiently increase the flexibility of the open-pore concrete layer and have inadequate crack bridging properties. Since rigid styrene acrylates of high MFT become brittle at low temperatures <10° C. and their performance is impaired, crack formation and grain escape occur in the uniform grain size concrete layer, resulting in poor durability, in particular after the winter period.
In WO 2008/052482 A1, a road surface of open-pore, polymer-modified concrete and a process for the production of such surfaces are claimed. The structure consists of a base course, bonding course, pervious concrete and surface treatment layer. For the polymer modification of the pervious concrete layer or the bonding course, any polymer dispersions are used. The structure has the disadvantage that a surface treatment layer is necessary to improve the wear of the pervious concrete layer and the skid resistance. This surface treatment layer is applied in the form of a polymer-modified mortar which can partly seal off the pores of the pervious concrete layer which has an adverse effect on the noise-absorbing properties and the drainage of the open-pore structure. Moreover, its application requires an additional working step, which adversely affects the economics.